1. Field of the Disclosure
The present disclosure relates generally to flow sensors and, more particularly, to intraluminal electromagnetic flow sensors for fluids such as blood.
2. Brief Description of Related Technology
Chronic measurement of fluid flow is useful for long-term monitoring of many diseases, including those related to the heart, kidney, bile duct, etc. In coronary artery disease, constrictions of blood vessels are commonly treated by a medical procedure called balloon angioplasty with stent implantation. However, re-closures often occur due to recoil of the blood vessels or further plaque deposition. Monitoring the blood flow can provide advance notice of such failures. Detection mechanisms proposed in the past for implantable sensors include thermal resistor, blood conductance, differential pressure, and acoustic methods.
Blood flow has also been measured using electromagnetic flow sensors, which have two electrodes across which a voltage proportional to the fluid velocity is induced in accordance with Faraday's Law. As conductive fluid passes through an applied magnetic field, the electromotive force is generated and detected by the two electrodes.
An electromagnetic hood flow sensor disclosed in Kolin, “An Electromagnetic Catheter Blood Flow Meter of Minimal Lateral Dimensions,” Proceedings of the National Academy of Sciences, Vol. 66, No. 1, pp. 53-56 (1970), utilized a catheter to place the two electrodes in the blood vessel. However, the catheter remains inserted throughout the measurement, rendering chronic, continuous, or long-term monitoring impracticable, if not impossible. Moreover, because the catheter remains inserted, the catheter and other aspects of the device must be small in size to, among other things, avoid inhibiting the blood flow. The small size of the device may then lead to insufficient flow sensitivity.
The principle of electromagnetic flow measurement has been demonstrated in connection with micro-sensors outside of the context of blood flow monitoring. For instance, in H. J. Yoon, S. Y. Kim, S. W. Lee, S. S. Yang, “Fabrication of a Micro Electromagnetic Flow Sensor for Micro Flow Rate Measurement,” SPIE Symp. Smart Struc. Mat., pp. 264-71 (2000), a sensor is disclosed that has a pair of silicon substrates having respective opposing faces that meet to form a flow channel. Despite the small size of the two substrates and the sensor as a whole, the deployment and use of the sensor in connection with a blood vessel may be complicated by the defined nature of the flow channel.